This description relates to high-voltage electrical switches.
Loadbreak switches, sometimes referred to as selector or sectionalizing switches, are used in high-voltage operations to connect one or more power sources to a load. High-voltage operations generally include those that employ voltages higher than 1,000 volts. Loadbreak switches may be used to switch between alternate power sources to allow, for example, reconfiguration of a power distribution system or use of a temporary power source while a main power source is serviced.
A loadbreak switch often must be compact in view of its intended uses (e.g., in an underground distribution installation, and/or in a poly-phase industrial installation internal to a distribution or power transformer or switchgear). The compact size of a loadbreak switch reduces the physical distance achievable between electrical contacts of the switching mechanism. The reduced physical distance between the electrical contacts, in turn, may make the switch vulnerable to sustained arcing in view of the high-voltage power to be switched. The problem posed by arcing may be especially acute at the time that contacts are being broken apart, for example, when a stationary contact and a moving contact are being disconnected. Arcing may occur between a power contact and ground, or between one or more power contacts. For example, in a three-phase switch, arcing may occur between one phase and ground, and/or between one or more of the three phases.
To reduce the incidence of arcing without increasing switch size, loadbreak switches often are submersed in a bath of dielectric fluid. The dielectric fluid is more resistive to arcing than is air. The dielectric fluid reduces but does not eliminate the distance required between contacts to suppress arcing. Hence, incidental arcing typically will occur until switch contacts are separated sufficiently to provide the required suppression distance. Although transient, such incidental arcing degrades the insulative qualities of the dielectric fluid by creating a path of carbonization elements and gas bubbles that is more conductive than the dielectric fluid. Repeated incidental arcing may bolster the conductive path, a path which eventually may provide a conduit for dangerous sustained arcing.
Sustained arcing may cause a loadbreak switch to fail catastrophically. More specifically, temperatures within the plasma formed by a sustained arc may reach tens of thousands of degrees Fahrenheit. Under sustained arcing, the dielectric fluid may vaporize and the metal contacts of the loadbreak switch may melt and/or vaporize, creating an expanding conductive cloud of high temperature ionized gas. As the conductive cloud expands, arcing may propagate to other contacts of the loadbreak switch which can create other fault paths between phases and phases to ground. Additionally, the conductive plasma and gases may expand explosively in an arc-blast as they are superheated by the sustained arcing. A breach in the seal of the equipment may result. In such an event, the arc-blast itself may exert a catastrophic force upon nearby surroundings. In addition to the superheated gases, the arc-blast may include molten metal and fragments of equipment transformed into projectiles.
In one general aspect, a high-voltage loadbreak switch operates submersed in a dielectric fluid and is configured to switch one or more phases of power and/or one or more loads using one or more phase switches. To help suppress arcing between different phases or between a phase and ground, a dielectric baffle intervenes about entirely between different phase switches, or may be provided to separate a phase switch from ground. Each phase switching mechanism includes first and second stationary contacts. The first stationary contact is connected to a phase of a high-voltage power source. Each phase switching mechanism also includes a non-stationary contact. The non-stationary contact may be placed in a first position to electrically couple the first stationary contact to the second stationary contact, and in a second position to decouple the first stationary contact from the second stationary contact. The non-stationary contact may be coupled non-switchably to the second stationary contact. The region of motion of the first non-stationary contact between the first position and the second position includes an arcing region. The high-voltage loadbreak switch uses a fluid circulation mechanism to circulate dielectric fluid through the arcing region.
Implementations may include one or more of the following features. For example, the fluid circulation mechanism may disperse conductive impurities (e.g., carbonization elements and/or bubbles) accumulated within the arcing region from past arcing. Circulation of the dielectric fluid at a sufficient rate also may suppress arcing by increasing by about ten percent or more a length of dielectric fluid an arc must traverse to pass through the arcing region. Circulation also may provide an enhanced flow of dielectric fluid that has not been exposed to arcing to improve quickly the dielectric strength in the arcing region.
The fluid circulation mechanism may include a paddle or paddles configured to increase the dielectric fluid flowing through the arcing region. The paddle may be formed of a non-conductive material, such as, plastic or fiberglass. The paddle may be included as part of the non-stationary contact or may be physically separate from the contact. The paddle and the non-stationary contact may be included as part of a rotor that is coupled to a rotatable shaft. Alternatively, or in addition, the paddle may be mounted directly to the rotatable shaft. In any case, rotation of the shaft may rotate the non-stationary contact between the first position and the second position while causing the paddle to circulate the dielectric fluid through the arcing region.
In another implementation, the high-voltage loadbreak switch induces a convection current with a heating element to enhance circulation of the dielectric fluid through the arcing region.
Other features will be apparent from the description, the drawings, and the claims.